1. Field of the Invention
The present invention relates to capacitive input devices installed in small and thin electronic apparatuses such as notebook computers, and in particular, relates to input devices having coordinate-inputting means and switching means.
2. Description of the Related Art
FIG. 6 is a cross-sectional view of a known input device shown in FIG. 4 in Japanese Unexamined Patent Application Publication No. 2002-351606. This input device includes a switching unit 9, a coordinate-inputting unit 7 with a coordinate-inputting section 7a, and a face sheet 8 with an operating surface 8a laminated in this order. In the coordinate-inputting unit 7, X-direction electrodes and Y-direction electrodes oppose each other in a grid arrangement with an insulative resin sheet 12 having a predetermined conductivity therebetween, and the resin sheet is disposed on a substrate having an electrically conductive pattern. The top surface of the resin sheet functions as the coordinate-inputting section 7a. The coordinate-inputting unit 7 can be deformed. The top surface of the face sheet 8 functions as the operating surface 8a, and marks such as “OFF” and “ON” and characters such as “1” and “2” are printed thereon. When part of the coordinate-inputting section 7a is pushed, a portion corresponding to that part is deformed. When a dielectric such as a finger comes into contact with the surface of the coordinate-inputting section 7a, the capacitances between the X-direction electrodes and the Y-direction electrodes are varied. Coordinate signals can be detected from these variations.
Meanwhile, the switching unit 9 is disposed below the coordinate-inputting unit 7, and includes a plurality of switches connected with each other in parallel and arranged on a switching-unit surface. The face sheet 8, the coordinate-inputting unit 7, and the switching unit 9 are superposed such that the positions of the switches correspond to those of inputting points 8b shown on the operating surface 8a. When the inputting points 8b on the face sheet 8 are pushed by fingers or pens, both the coordinate-inputting unit 7 and face sheet 8 are concaved. Since invertible plates 15 are concaved by the pushing force and come into contact with respective electrode components 13a1, 13a2 electrodes 13a and signal-connecting patterns 13b become conductive and the output is switched to ON.
More specifically, in the top face of the resin sheet 12, a circular electrode 13a1 and a ring-like electrode 13a2 are formed. An electric conduction pattern 13b on the opposite surface of the resin sheet 12 and in a resin pedestal 18 is connected with the electrode 13a1 through a conductor 14 in a through hole. A resist film 16a is disposed in the perimeter of the invertible plates 15 and separates a top resin sheet 17 from the resin sheet 12.
In order to provide an excellent tactile feel to operators operating the switches in the above-described input device, the invertible plates should be concaved with a smaller force, in other words, the pushing force given by the operators should be focused on the invertible plates.
However, in the above-described input device, marks (“OFF”, “ON”, and the like) and numerals (“1”, “2”, and the like) indicating the positions of the switches are printed on the operating surface of the face sheet. Therefore, the operators need to visually check the marks and the numerals, i.e. need to check the positions of the switches, during the switching operation; and the pushing force is hardly focused on the invertible plates.
Moreover, as described above, the coordinate-inputting unit is of a capacitance type that detects the position of the finger or the like on an XY-plane coordinates by detecting the variations of the capacitances as voltages by means of the capacitances generated among the finger or the like, the X-direction electrodes, and the Y-direction electrodes and varied in response to the transfer of the finger or the like. Accordingly, the capacitances are required to be accurate in inverse proportion to the distances between the finger or the like and the electrodes.
However, in the above-described input device, coupling capacitances are also generated between the invertible plates disposed under the coordinate-inputting unit and the electrodes. In addition, the variations of the coupling capacitances caused by each deformation of the invertible plates disadvantageously lead to a reduction in the accuracy of the detected coordinate positions.